Purpose: To validate prescription registry data as a measurement of adherence to statins through a direct method using assays for selected statins in serial blood samples collected from two prospective cohorts of Danish colorectal cancer patients.
Methods: We linked information on statin prescriptions from the Aarhus University Prescription Database with the cancer cohorts from Aalborg University Hospital. For statin-prescribed patients, we calculated a prescription window covering the anticipated duration of the prescription. For each statin-prescribed patient with at least one blood sample in a prescription window, we selected without replacement a never-statin-prescribed patient matched on sex, age, and calendar year of surgery. Each of the selected blood samples were analyzed using assays to detect statins. We calculated the positive and negative predictive value of the prescription registry reporting using the assay result as the gold standard.
Results: We identified 73 ever-statin-prescribed patients with a total of 253 blood samples and 74 blood samples among never-statin-prescribed patients. The positive predictive value for prescribed patients, with presence of statins in at least one blood sample as the gold standard, was 93% (95% CI, 86%-97%) and the negative predictive value was 93% (95% CI, 86%-97%). Stratified results did not reveal substantial differences in predictive values. Fifty-two (71%) of the statin-prescribed patients had statins in every blood sample, suggesting continuous adherence.
Conclusion: This study showed a high adherence with treatment with statins among colorectal cancer patients.
Keywords: adherence; health administrative data; pharmacoepidemiology; statins.
© 2019 John Wiley & Sons, Ltd.